After seeing The Big Showdown episode that recently dropped, I'm fascinated by the game and would love to see more.
My long-time position has been that the original Split Second and Three on a Match are two of the best game shows that have ever existed that have had the misfortune of being lost. If I had to cap it at three, those would be my picks.
If I can add more, I join the choruses for the original Sale of the Century, Jackpot and ABC Password.
If I'm allowed to add something we know exists but just hasn't gotten the rerun treatment, then seasons 4-10 of The Price Is Right, especially 1977-1979.
I don't know about Cross-Wits, but I've been told multiple times by reliable folks that master recordings of the entire run of Bill's Pyramid DO exist, but the owners don't want to go to the effort and expense of converting them.
I recall Adam saying the whereabouts of the tapes are unknown, and that is also part of the problem, unless I misremembered.